Significantly high molecular weight uncured elastomers (e.g. uncured elastomers of significantly high viscosity) are sometimes desired to prepare rubber compositions to achieve desired physical properties for cured rubber compositions, particularly for various vehicular tire components such as, for tire treads.
It is the organic solution polymerization prepared styrene/butadiene elastomers (SSBRs) that can achieve a desired high molecular weight (high Mooney viscosity) usually considered necessary to promote exceptional physical properties for the cured elastomer, particularly for use for various tire components, particularly tire treads.
However, accompanying the desired high molecular weight of the SSBRs is the significant increase in difficulty in processing the uncured elastomers both at the elastomer production facility, particularly for the finishing of the elastomer, and, also for the preparation of rubber compositions for use as, for example, various components of a tire because of the high Mooney viscosity of the uncured elastomer.
Therefore, such relatively high viscosity SSBRs are sometimes petroleum oil extended at the SSBR manufacturing facility to thereby reduce their viscosity and promote better elastomer processing at the SSBR manufacturing facility. Such SSBRs are often referred to as being oil extended SSBRs, namely petroleum oil extended. Exemplary of such petroleum based rubber processing oils are, for example, aromatic, naphthenic and paraffinic based oils, particularly their mixtures.
Accordingly, it is desired to evaluate whether addition of triglyceride based vegetable oils, instead of petroleum based oils could be used for suitably extending solvent solution prepared styrene/butadiene elastomers (SSBRs), particularly the high molecular weight (e.g. high Mooney viscosity) SSBRs.
Interestingly, it has been observed in such evaluation that use of a triglyceride based vegetable oil such as, for example, soybean oil extended organic solvent solution prepared styrene/butadiene elastomers having a relative high viscosity (Mooney viscosity) resulted in significantly lower viscosity for such uncured styrene/butadiene elastomer (SSBR) than a petroleum oil extended SSBR to thereby enable processing of an even higher molecular weight (even higher Mooney viscosity) SSBR. It is considered that such obtained lower viscosity for the uncured SSBR is both significantly advantageous and appeared to be essential to enable suitable processing for the SSBR at both the rubber manufacturing facility and at a rubber composition preparation facility.
Accordingly, it has been discovered that use of soybean oil instead of petroleum oil has resulted in better processing of a higher viscosity SSBR to promote better physical properties for the rubber composition containing such soybean oil extended SSBR.
Historically, a vegetable oil such as for example soybean oil, or soy oil, has been used for mixing with various rubber compositions by free oil addition to the rubber composition rather than soy oil extension of the elastomer at its point of manufacture. For example, and not intended to be limiting, see U.S. Pat. Nos. 7,919,553, 8,100,157 and 8,022,136. Soybean oil has also been used for oil extending emulsion polymerized elastomers for some circumstances. For example, see U.S. Pat. No. 8,044,118.
However, for this invention, it is desired to evaluate use of triglyceride based vegetable oils such as for example, soybean oil, for extending organic solvent solution polymerization prepared styrene/butadiene copolymer elastomers, particularly high molecular weight elastomers, during their manufacture.
For such evaluation, it is important to appreciate that various vegetable oils, including soybean oil, differ significantly from petroleum based oils, particularly where such vegetable oils are triglycerides which contain a significant degree of unsaturation and clearly not a linear or an aromatic petroleum based oil. Addition of such triglyceride to a cement of a freshly made SSBR contained in its solvent of preparation is considered herein as being of a speculative benefit without trial and evaluation.
The triglyceride(s) for vegetable oils such as, for example, soybean oil, sunflower oil and canola oil are in a form of esters containing a degree of unsaturation. Therefore, use of such triglyceride(s) containing a degree of unsaturation for treatment of a SSBR in its cement composed of the SSBR and organic solvent might be expected to promote a very different oil extended SSBR effect than use of petroleum based oil elastomer for such purpose which may necessitate modifications, hopefully beneficial modifications, of SSBR processing at the SSBR manufacturing facility and at the rubber composition preparation facility.
The following Table A is presented to provide a general illustration of relative saturated, mono unsaturated and polyunsaturated contents of various vegetable oils (triglyceride oils).
TABLE APercentPercentPercentVegetable OilSaturatedMono UnsaturatedPoly UnsaturatedSoybean162358Sunflower104540Canola (Rapeseed)76328Corn132855Coconut8762Cottonseed261852Olive147311Palm49379Peanut174632Safflower104540
Therefore, such use of vegetable oils for extending the SSBR in its solvent cement form may present requirements for potential modifications of sulfur cure packages for the vegetable oil extended SSBR because of additional unsaturation being present in the triglyceride oil as well as potentially presenting a different array of sulfur cured rubber physical properties for consideration when used with various rubber compositions for tire components as compared to petroleum based oil extended synthetic rubbers.
Such challenges are to be evaluated for triglyceride treatment of SSBR containing cement with results being unknown until the evaluation is undertaken.
In the description of this invention, the terms “compounded” rubber compositions and “compounds”; where used refer to rubber compositions which have been compounded, or blended, with appropriate rubber compounding ingredients. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).